Missions involve sending individuals and groups across boundaries, most commonly geographical boundaries, to carry on evangelism or other activities, such as educational or hospital work. Sometimes individuals are sent and are called missionaries. When groups are sent, they are often called mission teams and they do mission trips. There are a few different kinds of mission trips: short-term, long-term, relational and those that simply help people in need. Some people choose to dedicate their whole lives to mission. Missionaries have the authority to preach the Christian faith, and provide humanitarian aid.